For the purpose of improving the performance and the specific consumption of the propulsion engines of the aircraft, a new architecture is proposed which has a pair of contra-rotating, unducted propellers that are arranged either upstream or downstream of a gas turbine turboshaft engine. The engines are also referred to as “open rotor” engines. For example, the engine described in the patent application FR 2941493 comprises a conventional turboshaft engine gas generator, one or more turbine stages of which drive an unducted fan which extends outside the engine. In a turboshaft engine having a pair of downstream propellers, the rotors can also be mounted on a structural element downstream of the housing and driven by a free turbine by means of a gearbox, for example an epicyclic gearbox.
As in the case of conventional turboprop engines, the propeller blades of the open-rotor engines have a variable pitch, i.e. the pitch of these propellers can be modified during flight in order to change the thrust of the engine and optimize the output of the propeller in accordance with the speed of the aircraft. A number of devices have been conceived in order to vary the pitch of the blades, which devices generally comprise rotating the blade about the main axis thereof by means of conical pinions located below the root of the blade. The pinions engage with conical pinions of a control system.
During the flight phases, the pitch of a propeller changes between two limit boundaries which correspond to a low-pitch position at low travel speeds, for example of approximately 30° relative to the plane of rotation of the propellers, and to a high-pitch position at high speeds, for example of approximately 65° relative to this same plane of rotation of the propellers. The blades can assume a feathered position, which corresponds to a pitch which is greater than that of the high-pitch position and is equal to approximately 90°. In this position, the drag caused by the blades is minimal. The blades can also be placed in the thrust-inverting position and can have a negative pitch angle, −30° for example.
The pitch of the blades can be controlled by means of an actuator, the movable member of which is axially translated and rotates the pivots of the blades about the respective radial axes thereof by means of a suitable linkage which is mounted on a bearing.
Each of the two rotors of the pair of propellers has its own device for driving and for controlling the pitch. For the device of the upstream rotor, some of the stresses are linked to limiting the central space because of the need to provide a passage for the auxiliary systems of the rotor located downstream.
The object of the present disclosure is to provide an arrangement of the device for actuating the blades to rotate about the axis thereof, which arrangement is both compact and strong.